Unproductive Hens

I'll admit that I'm pretty frustrated with my backyard flock of hens. We haven't gathered an egg from these girls since November 3---a full two months without fresh eggs. Ours is a fairly common predicament. We have a couple of pullets who haven't arrived at maturity and aren't yet laying, and we have a few older hens who are stuck in the annual molt.

A chicken's annual molt, which occurs in the fall, lasts anywhere from a month to three or even four months depending on the age of the hen. The older a hen gets, the more stressful and time-consuming it becomes for her to shed old feathers and grow new ones. 

A spring chick will grow over the summer and begin laying eggs in the fall. She might experience a light molt her first fall, which will reduce her egg production but probably not halt egg laying entirely. She's likely to produce eggs her first winter and lay abundantly through spring and summer. But her second autumn will induce a more dramatic molt, and she is likely to stop producing eggs completely while her body works on growing new feathers. After the molt she'll start to produce eggs again, but her eggs will be larger and fewer than previously. As each year passes, her molt will become increasingly severe and her eggs less abundant.

As an urban farmer with a limit to flock size, how long do I continue to feed unproductive hens? Although the girls are obviously healthy and normal, when is it okay to cull the flock and raise new chicks? How can I justify the expense of chicken feed without any eggs?